Combine harvesters have been used for decades to cut and thresh crops such as wheat and corn. Mostly self-propelled these days, the typical combine comprises a frame supporting threshing/separating apparatus, a cleaning system (or shoe), an on-board tank for storing the collected grain, and an unloading system. A feederhouse is pivotally mounted to the front of the frame for supporting a cutting header and conveying crop material from the header to the threshing apparatus, generally by means of an enclosed chain and slat elevator. The general operation of combine harvesters is well known and will not be repeated here in detail.
The cleaning system normally includes a fan for generating a cleaning airstream which is directed through the falling grain to blow lighter chaff and the like out of the rear of the shoe. One common type of fan employed is a cross-flow fan which is arranged transversely (width-wise) in the front of the cleaning system, and often behind the combine rear axle. Air is drawn tangentially into a fan housing through a wide inlet which extends across the front of the housing, and exhausted generally rearwardly into the cleaning shoe.
To prevent plant material and the like from entering the cleaning airstream it is known to provide a debris screen across the flow path upstream of the fan air inlet. Due to the close proximity of the screen to the ground, the screen is prone to blocking as material, such as leaves, is held by the pressure differential on the surface of the screen. This problem is compounded by the trend for combines having larger and thus larger cleaning fans demanding higher airflows through the inlet. Once plugged, the combine must be stopped resulting in undesirable downtime and lost harvesting time.